With the continued development of vehicles capable of traveling at greater and greater speeds, there has been a continuing attempt to develop bumpers and other means to protect the vehicle body from damage upon impact. Many such bumpers have been developed in the past, but each is capable of only withstanding limited amounts of impact pressure without imparting substantial damage to the vehicle body.
For example, devices such as that disclosed in U.S. Pat. No. 1,438,177 to Hatashita have employed springs and other means for the temporary absorption of shocks imparted to the outer surface of bumpers, such that the spring then immediately returns to its initial position subsequent thereto. For this reason, as soon as the impact is greater than the tension on the spring, damage is caused to the front part of the automobile, as shown therein.
Furthermore, other such bumpers, including water-filled bumpers and hydraulic shock absorbers, of relatively high cost, have also been developed. Such bumpers, which normally cannot withstand impacts of greater than about 5 miles per hour, have thus led to the need for further developments. U.S. Pat. No. 3,694,019 to Carter discloses an energy absorbing bumper which can allegedly withstand low speed collision damage (approximately 5 miles per hour) and which relies upon the realignment of the molecules in certain synthetic thermoplastic materials during elongation to do so. These materials thus must be capable of being permanently elongated. Thus, when employing such a device, not only is a complex structure required, but after a single such impact complex methods for readjusting the device and removing the stretched material and replacing it with new material is required.
For these and other reasons there have been various attempts to employ new materials, and particularly various foamed plastic materials, for such purposes. Thus, U.S. Pat. No. 3,610,609 to Sobel discloses a deformable shock-absorbing bumper guard. The specific device of this patent includes both an encased rigid crushable cellular material and a flexible compressible material which returns to its normal position after impact. The encased crushable material of Sobel is " . . . totally encased . . . " in a housing, thus " . . . assuring density buildup upon impact of collision." Furthermore, the resilient material, or rubber, of this patent is intended to return to its normal dimensions when the colliding vehicle or body is removed.
Furthermore, U.S. Pat. No. 3,493,257 to Fitzgerald, et al, teaches an encased micro-cellular foam bumper including an inner high density foam material and an outer elastomeric coating thereon. This bumper is again intended to ". . . return to its original configuration . . . " after impact. Furthermore, the foamable material is cured to produce a tough elastomeric micro-cellular foam having a density of from 25 to 60 pounds per cubic foot, and which is integrally bonded to the elastomeric film thereabout.
In addition, U.S. Pat. No. 3,666,310 to Burgess, et al. is another shock absorbing bumper which includes a foamed plastic material therewithin. The patentee therein again teaches the necessity of employing high density foams, and particularly such foams which are "tight" foams having ". . . between about 90 and about 99% of the cells being of the open type . . . " The specific polyurethane foam employed by Burgess, et al. has a material density of over 7 pounds per cubic foot and preferably between 10 and 20 pounds per cubic foot, and is again encased within a rigid bumper assembly, or in certain embodiments by a high density skin, as in the prior Fitzgerald et al. patent. Again, therefore, the increase in density of the foam material during impact is also contemplated by this patentee.
Finally, U.S. Pat. No. 3,721,433 also to Sobel, teaches another deformable shock-absorbing guard for attachment to automobiles, this particular guard including an encased foamed plastic material, and preferably including different density components allegedly further aiding in accomplishing safe deceleration. The patentee thus employs various open cell rigid crushable foam-like materials, in addition to an 8 pound per cubic foot fine rigid and crushable closed cell foam-like material therein. The patentee specifically notes that these components are "completely enclosed and sealed in the housing."
It is therefore an object of this invention to provide an energy absorbing bumper which overcomes all of these deficiencies on such prior art bumpers.